"I began to hear gunshots, I made a radio call for help while running to the main entrance," Juma said.

"I took shelter in a residential compound until when I saw policemen come," adding that he had not seen the faces of the three men.

All the gunmen in the Westgate siege - understood to have totalled four, not the dozen that security forces initially reported - are believed to have died during the attack, according to security sources.

The Shebab said the gunmen came from a special suicide commando brigade.

They said it was a warning to Kenya to pull its troops out of southern Somalia, where they are fighting the extremists as part of an African Union force.

Interpol and the FBI have assisted Kenya in trying to identify four bodies believed to be those of the attackers.

However, a New York police report said the lack of concrete evidence of their death means that they may have escaped.

Two of the gunmen are named in court documents as Mohammed Abdinur Said and Hassan Abdi Dhuhulow, a 23-year-old Somali who spent time in Norway.

Like the attackers, the four on trial are all ethnic Somalis, but it is unclear whether they are Somali or Kenyan citizens.

Western officials have suggested that as many as 94 could have died in total in the attack.

Bodies were buried under tonnes of rubble after part of the mall's roof collapsed at the end of the raid following an intense fire that burned for weeks.